The invention relates to a blister pack comprising a base foil with at least one chamber closed by a rupture foil in such a way that the rupture foil is firmly connected to the base foil except for a limited area and a cover foil is disposed on top of the rupture foil which cover foil is less firmly attached to the rupture foil than the rupture foil is attached to the base foil so that the cover foil can be removed without affecting the rupture foil.
Such a blister pack is known for example from a brochure “Blister Lidding” of the company Lawson Mardon Singen GmbH. In this known blister pack, several areas of a base foil, each of which includes a chamber obtained by cupping, are separated from one another by grid-like arranged perforation lines. The chambers which generally receive medications are closed by an aluminum foil cemented onto the base foil. On the aluminum foil, a removable foil is disposed at its side remote from the base foil.
At the crossing points of the perforation lines circular areas are formed in which the aluminum foil is not connected to the base foil. In these so-called seal-free areas, the aluminum foil is not attached to the base foil so that it, and the removable foil disposed thereon can be grasped with the fingers.
The removable foil is disposed on the aluminum foil with a retaining force which is smaller than that with which the aluminum foil is mounted to the base foil. In this way, the removable foil can easily be removed from the aluminum foil without the aluminum foil being removed from the base foil.
Since the aluminum foil and the removable foil are so sized that the products contained in the chambers can be pressed through the rupturing aluminum foil only when the removable foil is removed, the removal of the products from the blister pack is difficult. Such blister packs are therefore called child-safe blister packs.
Although the removable foil is attached to the aluminum foil with a lower retaining force than the aluminum foil is attached to the base foil so that the removable foil can be removed from the aluminum foil, it happens quite frequently that, starting at the seal-free area, parts of the aluminum foil remain attached to the removable foil. Normally, the parts remaining attached to the removable foil have the shape of a wedge. In order to prevent the wedge from extending up to the chambers whereby the closure of the chambers would be detrimentally affected and the product would be at least partially exposed, the distance between the chambers and the seal-free areas must be correspondingly large. This however is disadvantageous since the pack must then be relatively large.
In order to avoid the formation of such wedge-like release of the aluminum foil, the aluminum foil has been perforated along a line extending between the seal-free areas and the chambers. As a result, the rip wedge should be interrupted at the perforated line so that it does not extend into the area of the chambers containing the medicine. In this way, the distance between the seal-free zones and the chambers can be reduced so that the pocket can be smaller but it has been found that the arrangement is not reliable that is the rip wedge is not reliably terminated at the perforation line. Often, a new rip wedge is formed starting at the perforation line which detrimentally affects the closure of the chambers.
It is the object of the present invention to provide a blister pack of the type described above which however is relatively small and with which the chambers remain sealed, with high reliability, when the removable foil is removed from the pack.